Non-Consolidated Affiliates (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Feb. 11, 2020	May 31, 2018	Mar. 31, 2017
Schedule of Equity Method Investments [Line Items]
Investments in non-consolidated affiliates	$ 454,936	$ 124,061
Distributions from non-consolidated affiliates	15,084	0	$ 0
Equity in income (loss) of non-consolidated affiliates	44,459	(32,517)	(7,023)
Distributions from non-consolidated affiliates	42,334	14,059	39,402
Avillion II | Merck Asset - Phase II Clinical Trial
Schedule of Equity Method Investments [Line Items]
Other commitment		19,000
Other commitments, percentage of costs (as a percent)						50.00%
Avillion II | AZ Asset - Phase II and Phase III Clinical Trial
Schedule of Equity Method Investments [Line Items]
Other commitment					$ 105,000
Other commitments, percentage of costs (as a percent)					44.00%
Equity Method Investment, Nonconsolidated Investee or Group of Investees | Legacy Investors Partnerships
Schedule of Equity Method Investments [Line Items]
Investments in non-consolidated affiliates				$ 303,700
Distributions from non-consolidated affiliates	22,700
Equity in income (loss) of non-consolidated affiliates	62,000
Equity Method Investment, Nonconsolidated Investee or Group of Investees | Avillion Entities
Schedule of Equity Method Investments [Line Items]
Equity in income (loss) of non-consolidated affiliates	(17,600)	(32,500)	$ (7,000)
Equity method investment, unfunded commitments	28,600	70,800
Equity Method Investment, Nonconsolidated Investee or Group of Investees | Avillion I
Schedule of Equity Method Investments [Line Items]
Distributions from non-consolidated affiliates	13,400	$ 14,100
Equity Method Investment, Nonconsolidated Investee or Group of Investees | Avillion II
Schedule of Equity Method Investments [Line Items]
Distributions from non-consolidated affiliates	$ 21,300